How are the Column Visibility elements stored in Accumulo

[Sitaraman Vilayannur]

Hi,
  How are the column visibility elements stored in Accumulo. Is there a
kind of compression that is used to save space or are all the elements for
each key value paired stored as is.
  A pointer to the region of the code that i should look at for the
implementation will also be helpful.
Thanks
Sitaraman